1. Field of the Invention
This invention relates to a crystallized glass for use in electronic components such as magnetic heads and the like.
2. Description of Prior Art
In recent years as electronic technology has progressed, demands for various kinds of glass have been increasing. Glass for magnetic head applications according to the conventional technology will be explained in the following:
FIG. 1 shows a typical construction of video tape recorder magnetic heads which use nonmagnetic substrates of ceramics.
Over the nonmagnetic substrate 1, a magnetic substance and SiO.sub.2 are laminated alternatively, forming a track section 2. The track section 2 is bonded to the nonmagnetic substrate 3 by crystallized glass 4. Two units of this set-up are put together forming a gap. The aperture of this gap is filled with gap glass 5.
In addition, the two units are bonded together by amorphous sealing glass. Coils are wound around a specified place of the structure. With the magnetic head thus constructed, the crystallized glass 4 must be crystalized sufficiently to prevent it from softening when bonding of the amorphous sealing glass 6 is taking place.
Amorphous alloys have been used so far as the magnetic substance. In this case, the working temperature of the crystallized glass 4 and the amorphous glass 6 is 480.degree. C. so as not to deteriorate the magnetic characteristics of the amorphous alloys.
Recently, however, corresponding to the magnetic recording media of high coercive force, superstructured nitride alloys composed of Co-Nb-Zr-Ta-N system or Fe-Nb-(Si-B)-N system (See, for example, the technical study reports MR-86-4, 87-14 and 88-55 of Institute of Electronics, Information and Communication Engineers of Japan) have been developed as the magnetic substance.
In these substances, a working temperature of 550.degree.-600.degree. C. is considered best so as to prevent deterioration of the magnetic performance of superstructured nitride alloys. In addition, the thermal expansion coefficient .alpha. of the magnetic substance is (100-110).times.10.sup.-7 /.degree.C.
Therefore, the working temperature of the required crystallized glass should be 550.degree.-600.degree. C. and the glass transition point which gives a yardstick to the maximum operating temperature after crystallization (after working) should be 550.degree. C. or more.
Also, the thermal expansion coefficient .alpha. of the crystallized glass should be a little bit smaller than that of the magnetic substance in order to create a compressive stress with the glass after its crystallization. Thus, .alpha. is preferably (80-100).times.10.sup.-7 /.degree.C.
Accordingly, a first example which achieved a performance close to the above, as described in Japanese Patent Publication Sho 48-22976/73, discloses a crystallized glass with a thermal expansion coefficient .alpha. of (93-95).times.10.sup.-7 /.degree.C. and a working temperature of 510.degree.-530.degree. C. under the amorphous state, and .alpha. of (80-82).times.10.sup.-7 /.degree.C. after working at a temperature of 510.degree..apprxeq.530.degree. C.
Also, a second example, which relates to commercially available crystallized glass, as in Corning Glass Work's products, shows .alpha. of 65.4.times.10.sup.-7 /.degree.C. and a working temperature of 525.degree. C. for Corning product number 7578. This product has a maximum operating temperature of 460.degree. C. after working. In other words, after working at 525.degree. C., product number 7578 crystallizes, and, once it crystallizes, it does not change its shape until the temperature becomes higher than 460.degree. C. In addition, an .alpha. of 47.6.times.10.sup.-7 /.degree.C. and a working temperature 580.degree. C. is obtained for Corning product number 7594.
A third example, as disclosed in U.S. Pat. No. 4,966,926 shows a crystallized glass of a SiO.sub.2 -B.sub.2 O.sub.3 -PbO-ZnO system which forms a crystal structure of Zn.sub.2 SiO.sub.4 and ZnB.sub.2 O.sub.4 at a firing temperature of 650.degree.-800.degree. C.
However, the above examples of glass have not been satisfactory in the following points:
The thermal expansion coefficient .alpha. is sufficient but the working temperature is too low as in the case of the above first example.
The working temperature is 500.degree. C. or more but .alpha. is too small and the maximum operating temperature is lower than 550.degree. C. after working as in the case of the above second example.
The crystallization requires heating at a temperature as high as 650.degree.-800.degree. C., as in the case of the above third example. This heating temperature does not comply with the working temperature requirement of 550.degree.-600.degree. C. as specified by this invention.